1. Field of the Invention:
This invention relates to an adjusting mechanism for optical instruments, such as microscopes, and particularly to an adjusting mechanism which incorporates a closed loop cable and pulley drive apparatus for moving one member relative to another. The adjusting mechanism may include a counter balancing device for counteracting the forces exerted on the adjusting mechanism.
2. Description of the Prior Art:
Precision optical instruments, such as microscopes, commonly use a combination of gears, or racks and pinions, or cams and followers, or a combination of these devices to move one member relative to another to gain focus. Some examples of microscopes having coarse and fine adjusting mechanisms for providing adjustment to the nosepiece relative to a fixed stage are illustrated and described in U.S. Pat. Nos. 3,135,817, issued June 2, 1964 to N. A. Wrigglesworth et al and 3,260,157, issued July 12, 1966 to O. W. Boughton. An example of a microscope having a stage adjusting mechanism may be found in U.S. Pat. No. 4,083,256, issued Apr. 11, 1976 to M. Shio. Wrigglesworth shows a cam and follower as does the patent to Boughton. The patent to Shio discloses a rack and pinion arrangement for moving the stage relative to the nosepiece.
In British Pat. No. 629,570, issued Nov. 11, 1949, a microscope adjusting mechanism is shown for displacing the nosepiece relative to the stage. The mechanism is intended to eliminate backlash and loss of motion, both of which have been common problems in the previously described microscope adjusting systems. The mechanism includes two flexible and non-extensible bands of thin metal, such as steel or phosphor bronze, which are connected together at right angles. One end of one of the flat flexible bands is connected to a pivotable member in contact with a nosepiece assembly. The free end of the second flat flexible band is connected to a worm sector. An adjusting shaft has a worm formed thereon which is engaged to the worm sector. Rotation of the adjusting mechanism in one direction exerts a pull on the flexible band members, causing the pivotable member to rotate and exerting an upward force on the nosepiece assembly, thereby moving the nosepiece away from the stage. A pair of springs are incorporated, one of which forces the nosepiece assembly in a downward manner. The other spring is of substantially stronger construction and pushes against the pivotable member to subject the flexible bands to a positive tensioning force.
In German Pat. No. 1,208,591, published Jan. 5, 1966, a mechanism is shown for counter-balancing an instrument part which is vertically movable along a track supported on a housing. In this mechanism, a spring is fixed at one end in the housing while its other end is coupled by a drive belt wrapped around a cam mounted cylinder drum to an idler pulley and then to the movable part. The tension of the spring may be altered by rotating the cam mounted cylinder drum. An overriding clutch is incorporated to prevent free running in the opposite direction.
In German Pat. No. 750,446, issued Dec. 21, 1944, an apparatus is shown for setting up observation microscopes for machine tools. In this apparatus, the microscope is not connected directly to the machine tool but, preferably is suspended from an overhead pendant cord hoist.
Examples of various other adjusting systems may be found in U.S. Pat. Nos. 3,019,707, 3,683,704, 3,768,885, 4,020,705 and 4,173,902.
The above described adjusting mechanisms suffer from a variety of problems, which may include numerous and sometimes expensive parts and which may require skilled technicians to assemble and adjust.
As will be detailed hereinafter, the adjusting mechanism of the present invention provides a solution to the problems set forth above. The mechanism incorporates a closed loop cable and pulley drive system which, where necessary, may be adjusted to counter balance various weights and forces exerted upon it. The closed loop drive system is economical to manufacture, easy to assemble and accurate within very tight tolerances. Additionally, the drive system of the present invention may be easily adapted to move either the stage or the head assembly, or for other applications.